TRANSITION-METAL TEMPLATED FORMATION OF [2]-ROTAXANES AND [3]-ROTAXANES WITH PORPHYRINS AS STOPPERS

The transition metal-directed threading of a molecular fragment contai ning a central chelate and an end-attached gold(III) porphyrin into a presynthesized coordinating ring affords a general precursor to rotaxa ne-type structures. After threading, construction of the second porphy rin acting as an efficient stopper affords a copper(I)-complexed [2]-r otaxane as well as a novel compartmental [3]-rotaxane. The latter comp ound consists of a three-porphyrin-containing molecular fragment threa ded through two 30-membered rings. Quantitative demetalation of the co pper(I)-complexed [2]-rotaxane affords a free-ligand [2]-rotaxane. The two porphyrins are bulky enough to inhibit any process leading to sep arate fragments, the cycle and the thread. H-1 NMR spectroscopy demons trates that upon decomplexation the [2]-rotaxane undergoes profound co nformation changes. Recomplexation using zinc(II) regenerates an entwi ned and compact structure similar to that of the copper(I)-complexed [ 2]-rotaxane obtained in the template reaction.